The present contact lenses are of two types: the soft hydrophilic and the hard hydrophilic. The soft hydrophilic lenses are currently made from crosslinked ethylene glycol monomethacrylate. The hard hydrophilic lenses are currently made from polymethyl methacrylate. The soft hydrophilic lenses are kept sterile by boiling because they tend to abosrb antimicrobial agents such as benzalkonium chloride and bind the antimicrobial agents into the lens structure and the lens becomes toxic to the ocular tissue. The hard lenses made from emthyl methacrylate do not absorb these antimicrobia agents and therefore may be stored in and cleaned with solutions containing preservatives such as benzalkonium chloride. Lenses made from methyl methacrylate are very hydrophobic and a wetting agent is required for the water to form a smooth layer on the surface of the lens. If no wetting solution is used, the water will form beads or droplets on the surface and prevent the lens from forming an image. The contact angle for methyl methacrylate is 60.degree. therefore each droplet will contact the lens surface at an angle of 60.degree.. A wetting agent will lower the wetting or contact angle to approximately 30.degree. which is within range of acceptability.
The plastic herein disclosed has a water contact angle of 30.degree. when hydrated. This provides a greater degree of comfort for the wearer and a reduction in surface friction and less foreign body sensation to the eye.
The material is hard and rigid which allows it to be manufactured by the techniques and processes which have evolved over the past twenty years in the contact lens industry. Polishing is the same as polymethylmethacrylate.
Contact lenses that are being used at this time depend upon the flow of lachrymal fluids around the edge of the lens to supply the cornea with its necessary oxygen. The cornea tissue maintains a temperature much lower than the other body tissues. This is due to evaporation at the corneal surface, and the lack of blood supply to the cornea. The temperature of the cornea must be at this lower level or its metabolic processes will be accelerated. The plastic now being used for fabricating contact lenses is a very poor conductor of heat. This insulating material covering a large percent of the corneal area raises its temperature which increases the chemical activity of the metabolic processes and the cornea demands more oxygen. The present lenses preclude the free exchange of atmospheric oxygen dissolved in the precorneal fluid from reaching the corneal tissue. The result is edema and epithelium disorganization.
Lenses have been made with small holes drilled through the lens in an effort to overcome this problem. If the holes are large, they will be seen by the wearer, and if small enough not to be seen, they become clogged with body secretions and are rendered useless.
The new and greatly improved contact lens of this invention overcomes these disadvantages by allowing dissolved gases to pass through the material from which the lens is made.